Due to its characteristics of being easily applicable to various products and electrical characteristics such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV) or a hybrid vehicle (HV) that is propelled by an electric motor. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A battery pack for use in electric vehicles generally has a structure consisting of a plurality of battery modules connected in series or in parallel, each battery module including a plurality of unit cells, to obtain high output. Also, the unit cell includes a positive electrode current collector and a negative electrode current collector, a separator, an active material, an electrolyte solution and a casing, and can be charged and discharged by electrochemical reactions between the components.
Also, the battery pack generally includes a battery management system (BMS) to monitor and control the state of secondary batteries by executing an algorithm for control of power supply to a driving load such as a motor, measurement of electrical characteristic values such as current or voltage, charge/discharge control, voltage equalization control, state of charge (SOC) estimation, and the like.
Recently, with the widespread use of a battery pack of a multi-module structure including a plurality of battery modules connected in series or in parallel, a method of integratedly controlling battery modules is used, in which a BMS is installed independently for each module and a correlation between BMSs is set on the basis of one master and multiple slaves.
A master unit set as a master BMS communicates with each slave unit set as a slave BMS to monitor the state of all the battery modules during charging/discharging of the battery pack, to collect electrical condition information (voltage, current, and temperature) of the battery modules each slave BMS manages and to transmit a control command necessary for voltage equalization or battery system protection or data required for the slave units.
For data transmission and reception, the master unit is connected to the slave units via communication lines, and data is transmitted and received using a communication protocol for the communication lines. As a related art, Korean Patent Application Publication No. 10-2012-0049225 discloses an example of transmitting and receiving data between units by way of serial peripheral interface (SPI) ports (see paragraph [0027]).
The SPI communication protocol needs at least two communication lines including a line for data transmission and reception and a clock line. Thus, when a failure such as disconnection occurs in any one of the two lines, even though the remaining communication line is in a normal connection state, data communication becomes impossible any longer.
The universal asynchronous receiver/transmitter (UART) enables communication using a single communication line. However, even in this case, communication may be disabled due to a failure in a central processing unit (CPU), for example.
Even though communication is disabled, if units are synchronized, voltage measurement or self-diagnosis is performed correctly and it is easy to know the content of data from the outside.
In contrast, even when communication is enabled, if units are not synchronized, each slave unit differs in timing of voltage measurement or self-diagnosis, so voltage measurement is not performed correctly or data obtained through voltage measurement may be unhelpful.
Accordingly, there is a need for a method that enables all units included in a communication system to do synchronized activities and perform data transmission and reception.